The body ply of a tire, also referred to sometimes as the carcass or carcass ply, extends from the bead portions, through both opposing sidewall portions, and the crown portion of the tire. One or more layers that include substantially inextensible materials referred to e.g., as cords are typically used in its construction. For a radial tire, these cords are typically oriented at greater than about 80 degrees as measured from an equatorial plane of the tire. In a pneumatic tire, the body ply helps constrain inflation pressure and determine the overall shape of the tire upon inflation. When the tire is inflated to a given pressure, the body ply will assume a particular shape or profile in the meridian plane that is referred to as the equilibrium curve.
Body ply design poses a challenge for all tires and particularly for wide-based single (WBS) tires, which are tires that typically have a relatively wide crown portion and may be used to replace a pair of tires each having a relatively narrow crown portion. All tires, particularly WBS tires, commonly have a difference in rigidity between the center of the tire and the shoulder region. This difference can be particularly pronounced as compared with either of the dual conventional tires that a single WBS tire replaces. The difference in rigidity can lead to uneven growth of the tire as it is inflated including differences in growth along the crown portion where the tread is located. As a result, the tire can experience enhanced motion of the shoulders compared with the center when the tire is rolling, which can create issues such as groove bottom cracking in the tread and an enhanced sensitivity of the contact patch shape to load variations.
Conventionally, the equilibrium curves used for tire design and construction are based upon a traditional three-ply membrane model. Unfortunately, because of the large difference in rigidity between the center and the shoulder region of the tire, particularly a WBS tire, this traditional model can yield a tire with uneven inflation growth. Again, this uneven inflation growth can create a flex point in shoulder of the tire, which can place large stresses on shoulder groove bottoms and reduce the rigidity of the shoulder region relative to the center of the tire.
Previous attempts to achieve even inflation growth have focused on e.g., adding structural stiffness to the belt package in the crown portion so as to mechanically restrain unwanted inflation growth. Unfortunately, this approach increases the cost of the tire as well as the mass of the tire. Increased mass can adversely affect tire performance such as rolling resistance.
Accordingly, a tire employing a body ply that provides for more uniform inflation growth would be useful. Such a tire that can have less differences in rigidity between the center and shoulders would be beneficial. Having these features in a tire such as e.g., a WBS tire that can also prevent or deter e.g., groove bottom cracking in the tread, decrease sensitivity to load variations, and/or provide other benefits would be useful. Achieving these advantageous benefits without increasing the mass or deleteriously affecting the rolling resistance or other performance criteria would be particularly beneficial. A method of creating or designing such a tire would also be useful.